In existing communication systems related to a Wideband Code Division Multiple Access (W-CDMA) scheme and a GSM scheme and the like, a center frequency of a band used for communication is defined to agree with a predetermined frequency called a raster or a frequency raster. The frequency raster is arranged on a frequency axis at every 200 kHz, for example. Therefore, a mobile station searches frequency rasters on the frequency axis in series (searches for each 200 kHz) so as to specify the center frequency of the operator so that the mobile station can connect to a downlink. Following non-patent documents 1 and 2 describe downlink cell search.    [non-patent document 1] 3GPP, TS25.101, “User Equipment (UE) radio transmission and reception (FDD)”, pp. 12-14    [non-patent document 2] Keiji Tachikawa, “W-CDMA mobile communication scheme”, MARUZEN, pp. 35-45